Researchers think a severe lack of oxygen, rather than trauma or infection, is likely to be involved in cases of Sudden Infant Death Syndrome (SIDS).

More than 100 infants annually die from SIDS in Australia but the rate has declined since studies revealed risk factors such as putting infants on their stomachs rather than backs.

Professor Roger Byard from Adelaide University says understanding the syndrome's biological process is a next step.

"You don't like to use the word 'breakthrough' but that's how I feel about it. For the first time we've got an independent verification that the hypoxia theory is probably the most applicable," he said of his team's latest work.

There are some babies who are particularly susceptible and we didn't know why and that's why we've been looking at the chemicals in the back of the brain and that's why I think this APP study really gives support to that direction.

Professor Roger Byard

The researchers came to understand a link with SIDS by studying a chemical reaction in the brain, looking at the presence and distribution of a protein called APP which accumulates or "stains" when there is injury to the nerve fibres.

Professor Byard thinks they might be closer to understanding the underlying mechanism of SIDS.

"The SIDS APP staining was quite different to the infectious group, it was quite different to the trauma group, but it was virtually identical to children and babies who'd died of suffocation and asphyxia," he said.

"That's not saying that SIDS babies die of suffocation and asphyxia, what it's saying is that the underlying mechanism could well be the same and that is a lack of oxygen."

He says while the staining does not tell the cause of death, it can help clarify how it happens.

"What we have been stumped by really is that we've got vulnerable babies. There are some babies who are particularly susceptible and we didn't know why and that's why we've been looking at the chemicals in the back of the brain and that's why I think this APP study really gives support to that direction."

Professor Byard says there are many theories on the cause of SIDS and he has ruled out some link with genetics.

"It may be that a genetic make-up of an individual plays a role. We'll be looking at that, but I think what we need to do is sort out what the actual problems are with the chemicals and then we can see how they're controlled," he said.

National CEO of SIDS and Kids, Leanne Raven, says the latest research finding is exciting news for support groups.

"SIDS is a diagnosis of exclusion, so when they cannot find any other reason why this infant is died they label it SIDS and of course the family, the parents, have no reason why this has happened and in that world of unknowns it makes it even harder," she said.

"If we can go out of business, find a cure for SIDS and you know stop it from happening, that's what we're about at SIDS for Kids."